validate international phone number in vb6 - vba

Question

I want validate international phone number in vb6 without using regular expressions
only () + this characters and numeric are allowed and it should be below 20 digits.
What I have tried:
private sub txtPhoneNo_validate ( cancel As boolean)
if txtPhoneNo = "" then exit sub
if not Isnumeric(txtPhoneNo) then
msgbox "phone number shold be in numeric only"
Elseif len(txtPhoneNo) > 20
msgbox "phone number shold be in numeric only"
Exit sub
end if
end sub
I want to add international format for validation in my code and () + this are the character only allowed
mainly i want to validate this kind of numbers [phone] [phone] 0779 345666 0208-3456667

Answer 1

The approach I would suggest, based upon your stated requirements, is to force the user to enter ONLY valid characters:
Option Explicit
Private Sub Form_Load()
txtPhoneNo.MaxLength = 20
End Sub
Private Sub txtPhoneNo_KeyPress(KeyAscii As Integer)
'allow only <backspace> <space> ( ) + - numeric
If Not (KeyAscii = 8 Or KeyAscii = 32 Or KeyAscii = 40 Or KeyAscii = 41 Or _
KeyAscii = 43 Or KeyAscii = 45 Or (KeyAscii >= 48 And KeyAscii <= 57)) Then
KeyAscii = 0
End If
End Sub
In summary, this code enforces a maximum length of 20 characters and discards the keystroke if the key is not a valid character.
This may be sufficient for your needs, but in reality it doesn't really validate the data. For example, the + could be entered anywhere in the textbox and still pass our validation. In other words, we are not completely enforcing the rules for international phone numbers. To do so would require much more code or the use of Regular Expressions.

Answer 2

The following answer ensures no more than "20 digits" are included, not just characters. It also ensures that '+' can only be in the leading position, "-" and " " cannot be in the leading position. While other solutions could be valid, if you wanted to keep with the _Validate() event, or if you want other checks than the basic ones, such as limiting '+' to only the beginning, this might be of use.
Private Sub txtPhoneNo_Validate(ByRef Cancel As Boolean)
Const MaxLength As Long = 20
Dim ANI As String, Cleaned As String
ANI = txtPhoneNo.Text
If ANI = "" Then Exit Sub
Dim I As Long, C As String
For I = 1 To Len(ANI)
C = Mid(ANI, I, 1)
If IsNumeric(C) Then
Cleaned = Cleaned & C
ElseIf C = "(" Or C = ")" Or (I <> 1 And (C = " " Or C = "-")) Or (I = 1 And C = "+") Then
' don't count these in count
Else
MsgBox "Phone Number should be contain only numbers, parenthesis, a leading plus, and spaces."
Cancel = True
Exit Sub
End If
Next
If Len(Cleaned) > MaxLength Then
MsgBox "Phone Number should contain at most 20 digits (provided: " & Len(Cleaned) & ")."
Cancel = True
Exit Sub
End If
End Sub

Answer 3

Use Regular Expressions from VB6. There are plenty of regex patterns for international phone numbers out there. Use work done and verified by others.